Ventilation
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Transcript of Ventilation
Topics covered
Ventilation
• Its importance
• Factors affecting Ventilation
• Types
–Natural Ventilation, Types
–Mechanical / Forced Ventilation, Types
–HVAC
–Hybrid Ventilation, Advantages & Disadvantages
VENTILATION
Ventilation – Free passage of clean air in a structure.
• The systematic removal of heated air, smoke, and gases
from a structure and replacement with cooler, cleaner
air.
• Ventilation includes both the exchange of air to the
outside as well as circulation of clean air within the
building.`
IMPORTANCE
• To reduce Carbon-di-oxide content in the air.
• To control dust and other impurities in the air.
• To suppress odours ,smoke ,concentration of
bacteria, etc.
• To remove the body heat generated or liberated by
the occupants.
• To maintain desired relative humidity.
• To maintain favorable ambiance to live-in…..
IN INDUSTRIAL ENVIRONMENTS, VENTILATION IS NECESSARY…..
To maintain an adequate oxygen supply in the work area.
To control hazardous concentrations of toxic materials in
the air.
To remove any undesirable odors from a given area.
To control temperature and humidity.
To remove undesirable contaminants at their source before
they enter the work place air.
APPLICATION OF INDUSTRIAL VENTILATION SYSTEMS
Optimization of energy costs.
Reduction of occupational health disease claims.
Control of contaminants to acceptable levels.
Control of heat and humidity for comfort.
Prevention of fires and explosions.
MINIMUM REQUIREMENTS
Sl.No. Nature of Building Rate of fresh air in m3 per head per hour
1 Factories, Workshops 15
2 Educational Buildings 23
3 Restaurants, Dining halls 25
4 Community Buildings 28
5 Theatres, Hospitals 35
6 Residential Buildings 50
7 Gymnasiums, Amphitheatres 80
FACTORS AFFECTING VENTILATION
• Air Changes(rate of air change = 3-5)
• Humidity(at 21c relative humidity = 30-70%)
• Quality of Air(odour ,organic and inorganic dust)
• Temperature(20c and 22c w.r. to winter and
summer)
• Use of Building(no.&age of occupants, working hrs)
TEMPERATURE EFFECTS Temperature inside a structure is often different from the outside ambient
temperature.
Maximum temperature differences occur when the indoor environment is heated.
Temperature differences cause differences in air density inside and outside,
which in turn produce pressure differences.
In the winter when indoor air temperatures are high relative to those outdoors,
the warmer and less dense air inside rises and flows out of the building at its top.
During hot weather when air conditioning produces lower temperatures inside
than outside, the reverse process occurs.
GUIDELINES FOR GOOD AIRFLOW
• Maximize air velocities in occupied rooms.
• Two openings on opposite sides increase airflow.
• Locate windows on opposite sides of the house.
• An inlet window smaller than the outlet creates higher inlet velocity
(e.g. 50% smaller)
• Horizontal window openings are more effective than square or
vertical openings
• Vertical air shafts or open staircases or roof ventilation can take
advantage of “stack effects” to increase airflow
VENTILATION - TYPES
• There are mainly two types of ventilation: natural and
mechanical.
• Natural ventilation includes the movement of outdoor air
through intentional openings such as doors and windows and
through unintentional openings in the building shell such as
cracks which result in infiltration and ex-filtration.
• Mechanical or forced ventilation is intentional ventilation
supplied by fans or blowers. These fans are usually part of the
buildings HVAC system which heats, cools, mixes and filters
the air being supplied to the building.
VENTILATION STRATEGIES
• NATURAL VENTILATION
– Flow driven by wind and temperature.
• FORCED AIR – MECHANICAL VENTILATION
– Exhaust ,Supply and plenum process.
• HVAC
– Mechanical cooling, heating and air conditioning.
• HYBRID VENTILATION
– Combinations of the above systems.
NATURAL VENTILATIONNATURAL VENTILATION
• This ventilation type is mostly used in smaller buildings .
• Normally it is driven by wind pressure and density variations.
• The various types are,
– single sided ventilation (density driven)
– stack ventilation (density driven)
– cross flow ventilation (wind driven)
STACK VENTILATION. (NATURAL)
This air is replaced by cold outdoor air that enters near the bottom of the building or
from the ground. This phenomenon is called the building “Stack Effect”.
NATURAL VENTILATIONNATURAL VENTILATION Influenced by:
– wind direction
– wind speed
– ventilation opening location
– interior/exterior temp. difference
– building geometry Etc....
19
TYPES OF NATURAL VENTILATION OPENINGS
Windows (Windows sliding vertically, sliding
horizontally, tilting, swinging).
Doors, monitor openings and skylights.
Roof Ventilators (weather proof air outlet).
Stacks connecting to registers.
Specially designed inlet or outlet openings.
FORCED VENTILATION• Mechanical or forced ventilation is used to control indoor
air quality.
• Excess humidity, odours, and contaminants can often be
controlled via dilution or replacement with outside air.
• Kitchens and bathrooms typically have mechanical exhaust
to control odours and sometimes humidity.
• Ceiling fans and table fans circulate air within a room for
the purpose of reducing the perceived temperature because
of evaporation of perspiration on the skin of the occupants.
TYPES
• Supply System
– Supplying fresh air by input fans in outside walls.
• Exhaust System
– Creating partial vacuum by exhaust fans and blowers.
• Plenum process
– Supply of fresh air by inlet ducts and exhaust of
vitiated air by outlet fans.
SUPPLY SYSTEMS
Components:
Air inlet section
Filters
Heating and/or cooling equipment
Fan
Ducts
Register/grills for distributing the air within the work space
EXHAUST SYSTEMS
Purpose:
An exhaust ventilation system removes the air and airborne
contaminants from the work place air
The exhaust system may exhaust the entire work area, or it may
be placed at the source to remove the contaminant at its source
itself
Types of exhaust systems:
General exhaust system
Local exhaust system
GENERAL EXHAUST SYSTEMS
Used for heat control in an area by introducing large
quantities of air in the area. The air may be tempered and
recycled.
Used for removal of contaminants generated in an area by
mixing enough outdoor air with the contaminant so that
the average concentration is reduced to a safe level.
LOCAL EXHAUST SYSTEMS(LES)
The objective of a local exhaust system is to remove the
contaminant as it is generated at the source itself.
Advantages:
More effective as compared to a general exhaust system.
The smaller exhaust flow rate results in low heating costs
compared to the high flow rate required for a general exhaust
system.
The smaller flow rates lead to lower costs for air cleaning
equipment.
What is the difference between Exhaust and Supply systems?
An Exhaust ventilation system removes the air and air borne contaminants
from the work place, whereas, the Supply system adds air to work room to
dilute contaminants in the work place so as to lower the contaminant
concentrations.
Plenum Process
HVAC
• Heating, ventilating, and air conditioning.
• The three central functions of heating, ventilating, and air-
conditioning which are interrelated, and provides thermal
comfort, acceptable indoor air quality, within reasonable
installation, operation, and maintenance costs.
• It can provide ventilation, reduce air infiltration, and
maintain pressure relationships between spaces.
Contd…• Heating
– Necessary in winter to supply heated air.
– Done by warm air furnaces, hot water circulation.
• Cooling
– Necessary in summer to supply cool air.
– Done by refrigeration, sprayers, cool water circulation.
• Air Conditioning
– Necessary for producing--CONDITIONED AIR
– Done by filters, precipitators, coolers ,humidifiers
Hybrid ventilation is a two mode system combining of natural ventilation and mechanical ventilation.
Mechanical ventilation is used when natural driving forces cannot fulfill the required ventilation level.
Hybrid Ventilation-Advantages
• Hybrid ventilation systems offer many advantages:– Relative low running costs for energy conditioning the ventilation
air
– Energy savings compared to full mechanical ventilation systems
– Easily controlled by the inhabitants compared to natural ventilation
– Relative low maintenance
– Reduced use of mechanical equipment compared to mechanically ventilated buildings
– Possibilities for night or passive cooling
Hybrid Ventilation-Disadvantages
• Disadvantages include:– Relative high initial costs
– Depending on climatic conditions, hybrid ventilation is not suitable for many types of buildings where mechanical ventilation might be the only solution
– Room space for equipment might be needed (space for ducting)
– Building design might impose restrictions to the use of hybrid ventilation
– The urban aspects (noise, outdoor pollution, wind velocity, humidity) might limit its use
1. Outdoor air2. Supply air3. Indoor air4. Transferred air5. Extract air6. Recirculation air7. Exhaust air8. Secondary air9. Leakage10. Infiltration11. Exfiltration12. Mixed air
Air flow in Mechanical ventilation
The air change rate refers to the number of times in a 1-hr period that the volume of air in a space is renewed.
Design Consideration:
The factors affecting air change rate are:
• The presence of air pockets or dead space in the Controlled area.
• The relative positioning of Supply and Return air grills.
• Type of Machine and Equipments placed inside the area
Air change rate
NATURAL VENTILATION• Natural ventilation is the ventilation of a building with outside air
without the use of a fan or any other mechanical system.
• It can be achieved with open-able windows or trickle vents when the
spaces to ventilate are small and the architecture permits.
• In more complex systems warm air in the building can be allowed to
rise and flow out upper openings to the outside (stack effect) thus
forcing cool outside air to be drawn into the building naturally
through openings in the lower areas.
• These systems use very little energy but care must be taken to ensure
the occupants' comfort.
NATURAL VENTILATION• Natural ventilation is the ventilation of a building with outside air
without the use of a fan or any other mechanical system.
• It can be achieved with open-able windows or trickle vents when the
spaces to ventilate are small and the architecture permits.
• In more complex systems warm air in the building can be allowed to
rise and flow out upper openings to the outside (stack effect) thus
forcing cool outside air to be drawn into the building naturally
through openings in the lower areas.
• These systems use very little energy but care must be taken to ensure
the occupants' comfort.